Check the dashpots side by side to make sure that the needles are at least visibly the same length and profile. Check the dashpot springs. Set the jets at the start visually so that they begin in the same place. I used a tyre tread depth gauge to get them spot on. A turn and a half down to start will be good enough. Set the mechanical linkage with the engine off so that the throttles open at the same time. (Some advocate a slight lead on one carb, but I've never used this method). Also adjust the choke linkage so the chokes activate together. So with the baseline set, you can start up, and warm up. Then first test the open throttle balance at say 2000 rpm, adjust if necessary and then adjust the idle balance. If you want to do the lift pin method, only lift it a quarter inch, not all the way. Adjust the jets the same amount each time to keep the relative position the same. That should sort the balance and mixture.
One colourtune will struggle with twin carbs if they have a balance pipe or manifold link, you really need two. But I've never managed to get the mixture right with colourtune, preferring the old fashioned way!
PS the spluttering at 4500 sounds like fuel supply, check the punp and filter if it has one.
